1. Field of the Invention
The present invention pertains to an improvement in fluorescence microscopes, and more particularly it relates to an improvement in incident light fluorescence microscopes.
2. Description of the Prior Art
Known incident light fluorescence microscopes are arranged, as shown in FIG. 1, so that the light rays coming from a light source 1 which is comprised of a mercury lamp or the like are passed through an exciting filter 2 (which allows only the light rays of a required specific wave length to pass therethrough) and these filtered light rays are then reflected on a dichroic mirror 3 to pass through an objective 5 and then impinge onto the object 6 which is made self-luminous. This object 6 absorbs those light rays having a specific wave length which impinge thereonto and emits light or fluoresces. This fluorescence is passed through the objective lens 5, the dichroic mirror 3 and a barrier filter 7 to be viewed through an eyepiece or eyepieces. In operation, the aforesaid object 6 is used after being dyed with a fluorescent dye. As such a dye, dyes for the fluorescence antibody technique, such as F.I.T.C. (Fluorescein Isothiocyanate) are widely used. Therefore, description will be made on instances where this particular dye is used in dyeing the object. This F.I.T.C. exhibits maximum absorption at the wave length of 490 m.mu., and emits maximum fluorescence at the wave length of 520 m.mu. which is close thereto. Accordingly, it is desirable to use such a dichroic mirror that reflects as much light rays of 490 m.mu. in wave length as possible and that passes as much light rays of 520 m.mu. in wave length as possible therethrough. In actual operations, there is being used a multi-layer interference filter which exhibits maximum transmission for the wave length of 520 m.mu. and has such a spectral characteristic as will cut off those light rays having wave lengths smaller than that. However, with the known incident light fluorescence microscope having such an optical system arrangement as that shown in FIG. 1, the luminous flux is caused to impinge onto the dichroic mirror 3 at the incidence angle of 45.degree.. Accordingly, in view of the optical property peculiar to such a multi-layer interference filter, it will be noted from the curve a in FIG. 2 that the maximum transmission decreases as compared with the instance of vertical incident light and also that the transmission shows gradual decrease towards those wave lengths smaller than that. In short, as will be clear from the curve a shown in FIG. 2, more than 50 percent of the light rays having the wave length of 490 m.mu. (which is equal to the wave length at which F.I.T.C. exhibits maximum absorption) are allowed to pass through the dichroic mirror so that the amount of light reflected decreases. In other words, there will be a substantial loss in the amount of light which illuminates the object to fluoresce. Also, in case of an object having a greater reflection factor, more than 50 percent of the reflected light of the fluorescent object will pass through the dichroic mirror. Such a light which passes through this mirror will give rise to the development of fogs, and there has been the drawback that the resulting image is dark and ambiguous.